The present invention relates to a method and apparatus for delivering a therapeutic agent to a localized internal tissue site within a patient. While various techniques are presently known in the prior art for such localized delivery of a therapeutic agent, a disadvantage in such techniques often exists in that the presence of the therapeutic agent is, often transient. The agent is typically washed away by moving fluids within the body, or quickly neutralized by biochemical processes.
Techniques are known to the art for the localized delivery of therapeutic agent by means of a small catheter which extends from the exterior of the patient to the internal tissue site, with a mechanical delivery system being provided to administer the therapeutic agent in a continuous, or periodic, controlled dosage over a substantial period of time. However, this requires the continuing presence of the catheter in the body, and the patient remains connected to the mechanical controlled delivery mechanism.
As another technique, controlled release members are surgically implanted into the patient, for example a plastic mass in which the therapeutic agent is impregnated. Such a controlled release member provides desired controlled release of a therapeutic agent, but the plastic carrier member remains as an implant after the therapeutic agent has been exhausted, unless it is removed, which may require surgery.
In accordance with this invention, a new method and apparatus for delivering therapeutic agent is provided, preferably for delivery in a controlled release manner over a substantial period of time at the internal tissue site. Thus, the internal tissue site can be bathed in the therapeutic agent for such a substantial period of time without the necessary presence of an indwelling catheter, and preferably without the presence of a residual implant which must be later removed.
The method of this invention may be performed in conjunction with other medical procedures. For example, it may be performed in conjunction with the well known PTCA procedure pertaining to the balloon dilation of coronary arteries to improve blood flow. It is the current custom in a PTCA procedure or related procedures to delivery by injection up to about 10,000 units of heparin as a bolus during or immediately after the procedure, with hourly or additional doses of heparin being administered up to 24 hours after the PTCA procedure.
However, it is known that such a systemic delivery of heparin has significant potential side effects that may contraindicate the PTCA procedure for certain patients i.e., those who are subject to internal bleeding such as ulcer patients, or patients with high blood pressure.
The purpose of providing a dosage of heparin to the patient immediately after PTCA or the like is to prevent the clotting of blood at the site where the artery was dilated by the balloon catheter in the procedure. By this invention, it become possible to administer overall a much lower effective dosage of heparin by administering it locally at the site of the arterial stenosis which was dilated by the balloon catheter. This is done by the application of heparin or other therapeutic agent directly to the stenosis site. Preferably, the therapeutic agent so applied can exhibit a controlled release characteristic for a long, effective life even after the PTCA catheter has been withdrawn.
Additionally, one in three patients conventionally have a restenosis within six months at the same arterial site, so that the coronary artery occludes once again, often putting the patient into worse condition than he was before the original PTCA procedure. In accordance with this invention it is possible during the original PTCA procedure to provide slow release therapeutic agents that reside in and adjacent the tissue of the stenosis to suppress not only thrombosis, but also subintimal fibromuscular hyperplasia, resulting in regrowth of the stenosis.
The invention of this application can be used in a wide variety of medical procedures above and beyond the dilation of stenosis in coronary arteries. One may provide therapeutic agents to a variety internal tissue sites where such is needed, preferably resulting in a persistent dosage of medication at the site. The medication and carrier, when used, is preferably removed by biochemical processes to leave no significant residue at the internal tissue site.
This invention relates to a method of applying a therapeutic agent to an internal tissue site of a patient, which comprises: advancing an elongated member such as a catheter internally into a patient to cause a portion of the elongated member to occupy the internal tissue site. A portion of the elongated member comprises a lateral wall section which carries the therapeutic agent in a manner permitting release thereof from the lateral wall section at the internal tissue site.
One then effects such release of the therapeutic agent at the internal tissue site. Such a step of effecting the release may make use of a catheter balloon as the portion of the elongated member that carries the therapeutic agent. Hence, by inflation of the balloon, the therapeutic agent is pressed into tissue of the internal tissue site, at least some of the agent being retained there as the catheter balloon is once again deflated.
Also, the therapeutic agent is preferably mixed with a controlled release carrier for the agent and positioned on an outer surface of the lateral wall section of the elongated member, which preferably is a catheter balloon is discussed above. Such controlled release carriers are preferably biodegradable over a relatively long period of time, so that as they are brought into contact with the tissues of the internal tissue site, preferably by balloon inflation, at least some of the therapeutic agent and carrier is retained there for a relatively slow, controlled diffusion of the therapeutic agent out of the carrier. Then, preferably, the biodegradable carrier is itself, in due time, removed by natural body processes.
Thus, it becomes possible to apply to an internal tissue site a persistent dosage of therapeutic agent which, with the carrier, provides a slow, controlled release over a predetermined time of the therapeutic agent to the nearby tissues. By this means, heparin, for example, can be provided in adequate dosage to a stenosis site after a PTCA procedure without the need to provide a full dosage of heparin to the entire body. Thus, patients who are subject to bade side effects of heparin are in less danger, while the desired effect of the heparin or other therapeutic agent on the stenosis site or other tissue is provided.
Examples of controlled release carriers which might be used include semisynthetic polyacryl starch microparticles (or other biodegradable microparticles containing the therapeutic agent), ethyl cellulose, poly L-lactic acid, heptakis (2,6-di-o-ethyl)-beta-cyclodextrin, polyalkylcyanoacrylate nanocapsules, polymethyl acrylate, monocarboxycellulose, alginic acid, hyaluronic acid, lipid bilayer beads (liposomes), polyvinylpyrollidone, polyvinylalcohol, hyaluronic acid, albumin, lipid carriers of continuous phase (nonmicroparticle type), and known agents for transdermal sustained release of therapeutic agents.
Appropriate carrier materials may be cross-linked to increase their persistence in the internal tissue site. The cross-link density may be adjusted to provide varying release rates of the therapeutic agent as may be desired.
Therapeutic agents may be applied in accordance with this invention by means of a catheter or other elongated member having the therapeutic agent carried on a lateral wall section thereof. Such agents may include any medication which would be desirably applied locally to a specific internal tissue site that can be reached by the catheter or other elongated member.
Specific examples of such therapeutic agents include anti-thrombogenic agents or other agents for suppressing stenosis or late restenosis such as heparin, streptokinase, urokinase, tissue plasminogen activator, anti-thromboxane B2 agents, anti-B-thromboglobulin, prostaglandin E, aspirin, dipyridimol, anti-thromboxane A2 agents, murine monoclonal antibody 7E3, triazolopyrimidine, ciprostene, hirudin, ticlopidine, nicorandil, and the like. Anti-Platelet derived growth factor may be used as a therapeutic agent to suppress subintimal fibromuscular hyperplasia at an arterial stenosis site, or any other inhibitor of cell growth at the stenosis site may be.,used.
The therapeutic agent also may comprise a vasodilator to counteract vasospasm, for example an anti-spasmodic agent such as papaverine. The therapeutic agent may be vasoactive agents generally such as calcium antagonists, or alpha and beta adrenergic agonists or antagonists. Additionally, the therapeutic agent may include a biological adhesive such as medical grade cyanoacrylate adhesive or fibrin glue, the latter being for example to adhere an occluding flap of tissue in a coronary artery to the wall, or for a similar purpose.
Also, a balloon catheter in which the balloon is expanded to apply a stent to the coronary artery or elsewhere may be provided with a coating of heparin or other anti-thrombogenic agent along the balloon, preferably in conjunction with a controlled release carrier for the agent. Thus, simultaneously with the application of the stent, the anti-throrbogenic agent is applied to the internal tissue site for preferably long term suppression of thrombogenic activity in the vicinity of the stent.
Additionally, the therapeutic agent in accordance with this invention may be an anti-neoplastic agent such as 5-fluorouracil or any known anti-neoplastic agent, preferably mixed with a controlled release carrier for the agent, for the application of a persistent, controlled release anti-neoplastic agent to a tumor site.
The therapeutic agent may be an antibiotic which may be applied by this invention, preferably in conjunction with a controlled release carrier for persistence, to an infected stent or any other source of localized infection within the body. Similarly, the therapeutic agent may comprise steroids for the purpose of suppressing inflammation or for other reasons in a localized tissue site.
The therapeutic agent may constitute any desired mixture of individual pharmaceuticals or the like, for the application of combinations of active agents.
The catheter or other elongated member may preferably be advanced into tissues of the patient toward the internal tissue site while the portion carrying the therapeutic agent is enclosed in a protective sheath, to prevent removal of substantial amounts of the therapeutic agent from the catheter before reaching the desired internal site. The, the protective sheath may be withdrawn, to expose the catheter portion which carries the therapeutic agent. Then the therapeutic agent is applied to the tissues, for example by expansion of a catheter balloon upon which the therapeutic agent resides, or by other processes such as spontaneous dispersion off the catheter into the tissues. If desired, the protective sheath may be a conventional introducer catheter, or it may be a split introducer sheath to facilitate removal of the sheath from the catheter after its withdrawal.